Question

Assertion :When a wire is stretched to two times its length keeping the diameter same, its resistance becomes $4$ times Reason: Resistance is directly proportional to length of wire

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

$R=\rho \frac{L}{A}$ $\Rightarrow R\propto \frac{L}{A}$

When length is stretched then area becomes half

So $R_N=\rho \frac{2l}{A/2}=4R$

Both statement are correct and reason is correct explanation of assertion .